Combustion of fossil fuels introduces emissions into the atmosphere, such as nitrogen oxides (NOx). NOx emissions arise from nitrogen present in the combustion air and from fuel-bound nitrogen in coal or fuel oil, for example. Conversion of fuel-bound nitrogen to NOx depends on the amount and reactivity of the nitrogen compounds in the fuel and the amount of oxygen in the combustion area. Conversion of atmospheric nitrogen, N2, present in the combustion air to NOx is temperature-dependent; the greater the flame temperature in the combustion area, the greater the resultant NOx content in the emissions. One way of reducing NOx content is to create a fuel-rich combustion area followed by a fuel-lean combustion area, which can be achieved by staging the introduction of air into the combustion chamber. Recirculating flue gas into the flame is another technique to limit NOx emissions.